U.S. patent number 7,171,312 [Application Number 10/698,042] was granted by the patent office on 2007-01-30 for chemical and biological agent sensor array detectors.
This patent grant is currently assigned to Smiths Detection, Inc.. Invention is credited to Tim Burch, Chang-Meng Hsiung, Neil Plotkin, Gregory Steinthal, Steven Sunshine.
United States Patent |
7,171,312 |
Steinthal , et al. |
January 30, 2007 |
Chemical and biological agent sensor array detectors
Abstract
Chemical and biological detector systems, devices and apparatus.
Such devices may be portable and wearable, such as badges, that are
analyte-general, rather than analyte-specific, and which provide an
optimal way to notify and protect personnel against known and
unknown airborne chemical and biological hazards. The devices of
the present invention are advantageously low-cost, have low-power
requirements, may be wearable and are designed to detect and alarm
to a general chemical and biological threat. A sensor device of the
present invention in one embodiment includes two or more sensor
devices, a processing module coupled to each of the sensor devices
and configured to process signals received from each of the two or
more sensor devices to determine an environmental state; and a
communication module that communicates information about the
environmental state to a user.
Inventors: |
Steinthal; Gregory (Los
Angeles, CA), Sunshine; Steven (Pasadena, CA), Burch;
Tim (San Gabriel, CA), Plotkin; Neil (Pasadena, CA),
Hsiung; Chang-Meng (Irvine, CA) |
Assignee: |
Smiths Detection, Inc.
(Pasadena, CA)
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Family
ID: |
35242323 |
Appl.
No.: |
10/698,042 |
Filed: |
October 29, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040204915 A1 |
Oct 14, 2004 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10624194 |
Jul 21, 2003 |
7034677 |
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60397135 |
Jul 19, 2002 |
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60422301 |
Oct 29, 2002 |
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Current U.S.
Class: |
702/32;
422/82.02 |
Current CPC
Class: |
B82Y
30/00 (20130101); G16H 50/80 (20180101); G08B
21/12 (20130101); G01N 33/0031 (20130101); G01N
33/0063 (20130101); G01N 33/0075 (20130101); Y02A
90/10 (20180101); G01N 33/48707 (20130101); Y02A
90/24 (20180101) |
Current International
Class: |
G01N
31/00 (20060101); B32B 5/02 (20060101) |
Field of
Search: |
;702/32,22,19 ;73/31.05
;422/82.02 ;340/522,573.1,511 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Ziegler et al., Bioelectronic Noses: A Status Report. Part II,
1998, Biosensors & Bioelectronics 13, pp. 539-571. cited by
examiner .
Porter et al., Sensor Based on Piezoresistive Microcantilever
Technology, 2001, Sensors and Actuators A 88, pp. 47-51. cited by
examiner .
McKennoch et al., Electronic Interface Modules for Solid-State
Chemical Sensors, 2002 IEEE, pp. 344-349. cited by examiner .
Zee et al., MEMS Chemical Gas Sensor Using a Polymer-Based Array,
Jun. 7-10, 1999, The 10th International Conference on Solid-State
Sensors and Actuators. cited by examiner.
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Primary Examiner: Nghiem; Michael
Assistant Examiner: Le; Toan M.
Attorney, Agent or Firm: Foley & Lardner LLP
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a continuation-in-part application of U.S.
patent application Ser. No. 10/624,194, filed Jul. 21, 2003 now
U.S. Pat. No. 7,034,677, which is a non-provisional of, and claims
benefit of, U.S. Provisional Application Ser. No. 60/397,135, filed
Jul. 19, 2002, both entitled "Non-Specific Sensor Array Detector
Badges", both of which are hereby incorporated by reference in
their entirety for all purposes. This application also claims the
benefit of U.S. Provisional Application Ser. No. 60/422,301, filed
Oct. 29, 2002, entitled "Nanomaterial-Based Large Scale Resistive
Arrays", which is hereby incorporated by reference in its entirety
for all purposes.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
NOT APPLICABLE
Claims
What is claimed is:
1. A biological agent detection apparatus, comprising: a substrate;
an array of two or more sensors arranged on the substrate, wherein
at least a first one of the sensors includes a sensing element
configured to detect a biological agent; a power module for
supplying power to the detection apparatus; a pick-up antenna,
wherein the power is supplied by an external RF field received by
the antenna; a processing module directly coupled to each of the
sensors and configured to process signals received from the two or
more sensors to produce an output signal; and a communication
module configured to provide information to a user in response to
the output signal having a value at or above a threshold value,
wherein the array of two or more sensors includes: an activating
unit configured to activate only one of said two or more sensors at
any point in time, in order to reduce power consumption of the
apparatus, wherein the activating unit comprises: at least one
shift register for selectively accessing one of the two or more
sensors; decoding circuitry for decoding an output of the at least
one shift register; a switch for receiving the decoded outputs of
the decoding circuitry, and for toggling a current based on the
decoded outputs; and a resistive sensor element for receiving the
toggled current, wherein the toggled current is utilized to access
only one of the two or more sensors at any point in time.
2. The apparatus of claim 1, wherein the processor is configured to
execute a first process that detects a change in an environmental
condition, and a second process that identifies an origin of the
change in the environmental condition.
3. The apparatus of claim 2, wherein the second process includes a
pattern recognition algorithm.
4. The apparatus of claim 1, further including a communication
module configured to provide the output signal to an external
intelligence device.
5. The apparatus of claim 4, wherein the communication module
includes one of a wireless interface and a physical bus interface
for communicating with the external intelligence device.
6. The apparatus of claim 5, wherein the wireless interface device
includes one of an RF transmitter, an RF transceiver, an IR
transmitter and an IR transceiver.
7. The apparatus of claim 5, wherein the physical bus interface
includes one of an RS-232 port, a USB port and a Firewire port.
8. The apparatus of claim 1, wherein the communication module
includes one of a LED, speaker, buzzer and vibration mechanism.
9. The apparatus of claim 1, wherein at least two of the sensors
are polymer composite sensors.
10. The apparatus of claim 1, wherein at least a second one of the
sensors is a chemical sensor.
11. The apparatus of claim 1, wherein the sensing element of the
first sensor is selected from the group consisting of a polymer
composite sensor, a surface modified carbon black sensor, a sol-gel
encapsulated enzyme, a biopolymer, a self assembling monolayer, an
intrinsically conducting polymer, a carbon nanotube composite, a
nanogold composite and a nanoscale polymer composite.
12. The apparatus of claim 1, wherein the apparatus has a dimension
of less than about 4 square inches.
13. The apparatus of claim 1, wherein the apparatus has a dimension
of less than about 1 square inch.
14. The apparatus of claim 1, wherein the sensors and the
processing module are integrated on the substrate.
15. The apparatus of claim 1, further including an attachment
mechanism for allowing a user to wear the apparatus.
16. The apparatus of claim 15, wherein the attachment mechanism
includes one of a clip and a pin.
17. The apparatus of claim 1, wherein the sensing element of the
first sensor is an intrinsically conducting polymer selected from
the group consisting of polyaniline and polythiophene.
18. The apparatus of claim 1, wherein the apparatus is used to
diagnose a disease or determine a biological agent based on
sampling the atmosphere or a bodily fluid.
19. The apparatus of claim 1, wherein a second one of the sensors
includes a sensing element configured to detect a biological
element different from the biological agent detectable by the first
sensor.
20. The apparatus of claim 19, further comprising a communication
module configured to communicate with an external processor.
21. The apparatus of claim 20, wherein the communication module
includes a wireless transmitter device.
22. The apparatus of claim 21, wherein the wireless transmitter
device includes one of an RF transmitter and an IR transmitter.
23. The apparatus of claim 1, further comprising a transistor
housed on the substrate and configured to reduce noise and switch
resistance for the two or more sensors.
24. The apparatus of claim 1, further comprising analog circuitry
configured to provide gain, baseline tracking and radiometric
sensing.
25. The apparatus of claim 1, further comprising: wakeup circuitry
coupled to the power module and configured to activate the two or
more sensors at periodic intervals, and to turn off the two of more
sensors at all other times between adjacent ones of the periodic
intervals.
26. The apparatus of claim 25, wherein the apparatus is maintained
in a lower-power-consumption ON mode during the all other times
between the adjacent ones of the periodic intervals.
27. A biological agent detection apparatus, comprising: a
substrate; an array of two or more sensors arranged on the
substrate, wherein at least a first one of the sensors includes a
sensing element configured to detect a biological agent; a power
module for supplying power to the detection apparatus; a pick-up
antenna, wherein the power is supplied by an external RF field
received by the antenna; a processing module directly coupled to
each of the sensors and configured to process signals received from
the two or more sensors to produce an output signal; a
communication module configured to provide information to a user in
response to the output signal having a value at or above a
threshold value; and a controlling unit configured to control the
processing module to cause the processing module to read out the
signals from the two or more sensors in a particular sequential
order, so as to prioritize certain sensors of the two or more
sensors with respect to other sensors of the two or more sensors,
wherein the array of two or more sensors includes: an activating
unit configured to activate only one of said two or more sensors at
any point in time, in order to reduce power consumption of the
apparatus.
Description
BACKGROUND OF THE INVENTION
The present invention relates to detector systems for chemical and
biological sensing. The present invention also relates to small
form factor, portable, handheld and wearable detector systems and
in particular to portable, handheld and wearable detector systems
including sensor arrays configured for biological and chemical
analyte detection, and which are configurable with software modules
to detect and analyze a variety of environmental conditions and
which have low operating power requirements and long lifetimes.
Civilian and military personnel, Coast Guard and Customs, State and
Federal Emergency Responders, and Industrial Workers would greatly
benefit from a personal early-warning system to identify changes in
environmental conditions, such as the release of hazardous airborne
chemicals or biological agents, in time to either evacuate or don
protective equipment, such as chemical protective equipment (CPE).
For example, releases of toxic industrial chemicals (TICs) may
occur accidentally in the course of normal operations, from unseen
leaks in fueling, heating or cooling systems, or from intentional
hostile actions. Additionally, chemical warfare agents (CWAs) and
biological warfare agents (BWAs) may be released during combat or
in other potentially hostile situations such as during terrorist
activity. Each of these situations presents a unique and
potentially broad range of chemical and biological threats that
typically cannot be identified a priori. There is a need to detect
and characterize TICs, CWAs, BWAs and other environmental
conditions before hostile exposure in order to take appropriate
actions to neutralize the threat. A similar need exists after a
TIC, CWA or BWA release to identify the chemical or biological
agent class such that appropriate defensive and decontamination
measures may be taken.
While laboratory instruments with high specificity and accuracy are
available, they are not generally suitable for field use because
they lack physical robustness, require highly trained operators,
and typically are not portable due to size, weight, high power
consumption requirements, and chemical reagent (gases, liquids)
requirements. In addition, specialized portable instruments for one
threat type, (e.g. CWA) may not work for the other threat types of
interest, (e.g. explosives, fire, BWAs or TICs) or for improvised
devices.
Handheld as well as wearable, passive detectors for hazardous
conditions such as TICs, BWAs and CWAs will greatly improve the
safety of the personnel operating in threatened environments.
Useful known portable detectors include point detectors and
standoff detectors. One chemical point detector, the Joint Chemical
Agent Detector (JCAD), is hand held and portable but has a limited
operational life on a single charge, requiring frequent recharging.
In addition, the JCAD has to be handled impairing use of other
devices simultaneously. Standoff detectors, such as the Joint
Services Lightweight Standoff Chemical Agent Detector (JSLSCAD),
can continuously protect personnel from CWAs, but (1) lack spatial
resolution and (2) have detection limits much larger than the
Immediately Dangerous to Health and Life (IDLH) level. General
limitations of current badge or wearable detectors (e.g., SafeAir,
ToxiRAE) include: 1) analyte-specificity: these require detailed a
priori knowledge of chemical hazards, or multiple badges for broad
spectrum coverage, and cannot detect new or unknown hazards; 2)
single-use: disposable detectors and dosimeters require re-supply
for continuous protection; 3) interpretation errors: colorimetric
indicators require visual comparisons (color cards) that are prone
to user subjectivity; 4) no alarm modes or communications
capability: these do not provide rapid hands-free warning or
transmission of status; 5) environmental performance: extremes of
temperature (e.g., <0.degree. or >40.degree. C.) and humidity
(e.g., <10% or >90% relative humidity (RH)) limit some
sensors (e.g., electrochemical, conducting polymers). Such
detectors also do not typically include datalogging capability
(e.g., storing detailed historical information/records of the
environment encountered), or may only provide a time-averaged
history of exposure. Additionally, current detectors also typically
have high operational power requirements and, therefore, typically
short operational lifetimes. For example, the JCAD requires
recharging or replacement of the power supply every 20 hours or
less.
Some sensor devices, such as the ToxiRae Plus, produce audible and
vibratory alarns, eliminate interpretation errors, and have
datalogging capability, but these wearable sensors are still
analyte-specific. In addition, these sensors are not useful as
badge detectors since they require a pocket or belt clip due to
their size and weight.
Wearable sensor devices with analyte-general capability have been
developed, e.g., by EIC Laboratories, Inc. and Physical Sciences,
Inc., however these devices have significant performance issues
with humidity that are likely to affect the ruggedness and
stability of the sensors during field-use of the badge
detector.
While improvements have been made in the field of chemical and
biological sensing, the diverse set of potential target compounds
and numerous sensing methodologies has limited progress. Most
current low-cost sensors are based on a single sensing approach
optimized to detect one, or a class, of compounds.
On the biological side, significant recent research has been
directed toward fluorescence-based arrays for genomic and
proteomics applications (Kristensen et al., Biotechniques,
30(2):318 (2001); Harrinton, et al., Curr. Opin. Microbiol,
3(3):285 (2000); Katsuma et al., Expert Rev. Mol. Diagn., 1(4): 377
(2001); Templin et al., Trends Biotechnol, 20(4):160 (2002);
Schweitzer et al., Curr. Opin. Biotechnol, 13(1):14 (2002); Gabig
et al., Acta Biochim. Pol., 48(3):615 (2001); Weinstein et al.,
Cytometry, 47(1):46 (2002)). These arrays all focus on a single
sensing approach, most often related to binding of a fluorescent
probe. Because of the complex nature of reading and interpreting
these arrays, they are always associated with laboratory based
analytical instruments and are not compatible with widely
distributed sensing networks.
While high density sensor arrays have recently been developed for
biological detection, these sensors often require a significant
amount of wet chemistry prior to detection and are based on
relatively complicated and expensive read out electronics such as
optical readers. Furthermore, since these arrays rely exclusively
on specific binding, these arrays are not effective chemical
sensors and require a great deal of customization of each sensor
element.
There is therefore a need for improved sensors and detector systems
for biological and chemical sensing. There is also a need for
personal detector systems (e.g., portable and wearable detectors)
that overcome the limitations of current detectors and which
provide personnel with continuous, reliable protection in a
potentially dangerous environment. The present invention satisfies
these and other needs.
BRIEF SUMMARY OF THE INVENTION
The present invention provides improved biological and chemical
analyte detection systems and devices. The present invention also
provides portable and wearable detector systems and devices, such
as badges. In certain aspects, such systems and devices are
analyte-general, rather than analyte-specific, and therefore
provide an optimal way to notify and protect personnel against
known and unknown environmental conditions and events such as
airborne chemical and biological hazards, without the device having
to be handled. Such devices according to aspects of the present
invention are advantageously low-cost, have low-power requirements,
may be wearable and are designed to detect and alarm to a general
environmental threat.
Devices according to one aspect of the present invention include
software modules configured to analyze sensor signals to provide
for detection and identification of a variety of environmental
conditions such as, for example, a release of TICs, BWAs and CWAs.
Such devices therefore advantageously allow for protecting more
individuals at lower cost and without specialized training than
expensive point detectors, stand-off area monitors, or existing
detector badges that are limited to single chemical detection.
According to another aspect, devices of the present invention
include communication modules and are implemented in a network,
such as a distributed network of sensor devices.
As used herein, an environmental event, condition or state may
include, for example, an environmental parameter such as
temperature, humidity or pressure, radiation level, or other
physical stimuli, the presence or a level of an atmospheric
constituent such as an airborn chemical or vapor, the presence or a
level of a liquid or fluid constituent such as a chemical, a
biological agent or material, a therapeutic agent, and others. A
change in an environmental state or condition may include an
increase or a decrease in the level or presence of an environmental
parameter.
In certain aspects, detector devices of the present invention
include one or more of the following features or attributes: uses a
non-specific sensor array to detect one or multiple environmental
conditions, e.g., TICs and CWAs at IDLH levels, uses
polymer-composite sensors which are stable in the presence of
moisture, measures relative humidity and ambient temperature, can
be used in a wide range of operating conditions (relative humidity:
0 99% non-condensing; temperature: -15.degree. C. to 40.degree. C.
or greater) is passive and requires no user-interaction or
user-attention during field-use, includes downloadable flash memory
to maintain an historical data record, provides an audible alarm
and inaudible alarm when TIC, BWA or CWA is detected, includes an
audible and inaudible periodic signal during normal operation, is
smaller than a credit card and weighs ounces, has a battery
lifetime of at least two weeks or more (e.g., multiple years)
during continuous field-use, has at least a two-year shelf-life,
meets the requirements for high-volume manufacturing, has a low
cost of goods and services (e.g., approximately $30 rough order of
magnitude) for large volumes, can be directly integrated into
existing products (e.g., wireless sensor networks for detecting
industrial chemical leaks and the release of CWAs in public
facilities) to increase the available market size.
According to certain aspects of the present invention,
polymer-composite sensor technology is used to construct arrays of
two or more sensors useful for various applications, such as
portable or wearable detector devices for detecting and analyzing
environmental conditions and changes therein such as the presence
of TICs, BWAs and CWAs. Such devices including PCS sensors are
particularly advantageous as they can be configured to be compact,
light-weight, wearable, rugged, stable, low-cost, low-power, and
analyte-general. Polymer-composite sensors do not have the same
humidity-performance limitations as conductive-polymer sensors.
Since polymer-composite sensors are low-power sensors rather than
no-power sensors (e.g., current off-the-shelf (COTS) badge
detectors), detector devices according to certain aspects of the
present invention are able to produce alarms with no interpretation
errors and allow for datalogging capabilities. By combining a
sensor array with techniques for detection and identification,
detector devices according to certain aspects of the present
invention are advantageously non-analyte-specific, addressing
another limitation of current COTS detectors and others.
According to an aspect of the present invention, a biological agent
detection apparatus is provided. The apparatus typically includes a
substrate, and an array of two or more sensors arranged on the
substrate, wherein at least a first one of the sensors includes a
sensing element configured to detect a biological agent. The
apparatus also typically includes a processing module, directly
coupled to each of the sensors, configured to process signals
received from the two or more sensors to produce an output
signal.
According to another aspect of the present invention, a sensor
system is provided. The system typically includes a plurality of
sensing devices, each device including an array of two or more
sensors arranged on a substrate and a wireless communication module
for remote communication. The system also typically includes a
central processing node, located remote from said sensing devices,
including a processing module and a communication module, said node
being configured to receive and process signals from the plurality
of sensing devices.
Reference to the remaining portions of the specification, including
the drawings and claims, will realize other features and advantages
of the present invention. Further features and advantages of the
present invention, as well as the structure and operation of
various embodiments of the present invention, are described in
detail below with respect to the accompanying drawings. In the
drawings, like reference numbers indicate identical or functionally
similar elements.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a and b illustrate a representation of a composite detector
material responding during an analyte exposure, and a
representation of how data are converted into response patterns,
respectively according to an aspect of the present invention.
FIG. 2 is a chart which illustrates IDLH levels of various agents.
In this chart, the points denote concentrations of Immediately
Dangerous to Life and Health (IDLH) levels. Chemical warfare agents
and toxic industrial chemicals are shown. Chemicals with points
above the region for the minimum detectable level have a high
probablity of being detected at IDLH levels by the sensor array in
a sensor arrangement such as a Cyranose.TM. 320 (C320), for
example. Chemicals having points within the region have a moderate
probability of being detected at IDLH levels, while chemicals
having points below the region have a low probability of being
detected at IDLH levels
FIGS. 3a and 3b illustrate portable detection devices according to
embodiments of the present invention.
FIG. 4 shows a typical response curve to a transient event. In this
case the response curve depics, merely by way of example, a
four-channel chemical-event detector being exposed to a transient
chemical response.
FIG. 5 shows an example of a detector device according to an
embodiment of the present invention. In this instance and by way of
example only, the detector device is a four-channel chemical event
detector.
FIG. 6 shows an example of a fire detection system including
detection devices according to an embodiment of the present
invention. In this instance, the nodes are defined as a collection
of sensors/detectors at a single physical location, while the zones
are defined by physical relationships between the nodes. This, in
this instance, provides a mulit-level architecture for data
analysis which renders the system both flexible and scalable.
FIG. 7 shows a typical response for a device using 32 sensors. The
graph shows response as a function of time for the UL Wood Crib #1
fire.
FIG. 8 illustrates a model using Soft Independent Modeling of Class
Analogy (SIMCA). In this instance the model is, merely by way of
example, for fire and nuisance tests that exceed a positive
threshold. The line seperating these two regions is drawn to
minimize the number of false negatives such as the case wherein the
actual event is, by way of example, a fire but no alarm is
sounded.
FIG. 9 llustrates examples of chemical filter systems for which an
end-of-service-life indicator (ESLI) module including one or more
PCS sensors are useful.
FIG. 10 illustrates a system for remote detection and notification
in airport terminals including a distributed network of wireless
sensor devices according to an embodiment of the present
invention.
FIG. 11 illustrates a schematic representation of a Residual Life
Indicator Fixture according to an embodiment of the present
invention.
FIG. 12 illustrates a mask-based filter interface system including
a detector device module according to an embodiment of the present
invention.
FIG. 13 shows signal to noise ratio measurements for multiple
sensors.
FIG. 14 shows addressing for a sensor array according to one
embodiment.
FIG. 15 shows a sensor cell according to one embodiment.
FIG. 16 shows the I-V response of the cell of FIG. 15.
FIG. 17 shows the response of the cell of FIG. 15 to octanol.
FIG. 18 shows an adaptive bias circuit according to one
embodiment.
FIG. 19 shows a table of four SMCB materials.
FIGS. 20a and 20b show the chemical structures of
polyanilinapolyaniline and polythiophene, respectively. FIG. 20a
depicts the chemical structure of polyaniline in its insulating
state and its conducting state following protonation by an acid HX,
while FIG. 20b shows the chemical structure of
poly(3-subsituted-thiophene) wherein R=H, or alkyl, and wherein
[OX]=oxidizing agent, in its insulating state and its conductive
state (following oxidative "doping").
FIG. 21 illustrates a sol-gel encapsulation process as a schematic
diagram of a sol-gel encapsulation of indicator biomolecules,
wherein (a) shows the formation of sol particles during initial
hydrolysis and polycondensation; (b) shows the addition of
indicator biomolecules to the sol; (c) shows the growing silicate
network beginning the trap the biomolecules; and (d) shows the
indicator biomolecules immobilized in the gel.
FIG. 22 illustrates a power management method according to one
embodiment.
FIG. 23 illustrates a detection process and a typical response
curve according to one embodiment.
FIG. 24a shows the correlation between traditional and breath-based
diagnoses.
FIG. 24b shows discrimination of bacteria according to one
aspect.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an integrated resistance-based
chemical and biological sensing system on a silicon chip. Such
chips according to the present invention are advantageously
low-cost, low power, small, rapidly responding devices that can
detect, classify, quantify, and track a wide variety of chemical
and/or biological species in air or other carrier medium. Such
devices are able to detect these species at concentrations of up to
three orders of magnitude lower than current low-cost sensor
technology. These chips are also advantageously consistent with
distributed networks, such as low-cost (<$5 per node),
self-assembling, wireless networks, such that chemical and
biological sensing may become as ubiquitous as temperature and
pressure sensing. Such devices result in enhanced safety, improved
manufacturing, and a cleaner environment.
The present invention exploits a number of chemical and biological
sensing technologies that are VLSI compatible and which have a
number of superior chemical sensing performance properties relative
to most previously available systems. Sensing materials include
nanoparticle composite sensors such as polymer composite sensors,
sensors based on nanotubes, and sol-gel based biological sensors
(biogels). In addition, intrinsically conducting polymer sensors
are also used. The present invention also provides fabrication
techniques for the deposition of nanoliter size drops of these
complex composite materials. The present invention also provides a
number of solutions or suspensions of sensing materials that are
stable dispersions at the nanometer size regime.
The present invention provides a broadly useful chemical and/or
biological sensor that can be utilized across a wide range of
applications and therefore drive volumes that may result in
extremely low-cost sensing. Chemical and biological sensing is
generally relegated to laboratories using highly sophisticated
instruments or to point measurements using hand-held devices. No
broad-based, low-cost, sensing technology exists that can be easily
deployed across a wide range of applications (as a pH meter or gas
chromatograph can be in the laboratory setting). Since each
potential application has limited volumes, very low-cost devices do
not exist, except, for example, carbon monoxide sensors which have
been adopted on a much wider basis.
Applications for this low-cost solution are numerous and include,
but are not limited to, fire protection, leak detection, filter bed
monitoring and medical diagnosis. Each of these applications is
characterized by a wide range of potential target compounds. A few
examples are mentioned below but the overall economic impact goes
well beyond those listed.
Detector devices according to the present invention preferably
include an array (i.e., at least two) of polymer-composite sensors.
A polymer-composite sensor (PCS) typically includes a conducting
media, a polymeric phase, and two electrodes. When a voltage is
applied across the electrodes, electrons travel across the sensor
via pathways consisting mainly of the conducting media, and sensor
resistance is measured. Sensor resistance is one of the simplest
measurements of the state of the sensor and is related to the
number of molecules sorbed in the sensor--a change in sensor
resistance is proportional to a change in the mass of sorbed
molecules. In certain aspects, The PCS sensors, or other sensors in
an array of sensors, are modified as described herein to optimize
chemical and/or biological analyte detection. For example, in one
aspect, a specific receptor is grafted, or otherwise attached, to
the surface of a conductive particle for specific biodetection
applications. As another example, traditional electrodes are
replaced with microfabricated vertical carbon nanotube electrodes
in one aspect. The nanoscale size results in a small time constant
and a low ohmic drop, thereby enhancing detector sensitivity.
In a PCS sensor, when there is a change in the chemical vapor that
is in contact with a sensor, there is a concomitant response such
as a change in sensor resistance. A change in the vapor phase
causes a change in the chemical potential of its components and a
subsequent difference in chemical potential between the sensor and
the vapor phase. This difference in chemical potential results in a
net transport of molecules into or out of the sensor, depending on
whether the vapor or the sensor has greater chemical potential for
that component. This net transport of molecules causes a change in
the resistance since the number of sorbed molecules in the sensor
changes, and the net transport continues until the chemical
potential of all components is the same in the vapor and sensor.
FIG. 1A shows a representative sensor response to a step change in
the concentration of an analyte. For a period of time, the sensor
is exposed to air and the sensor resistance, R.sub.baseline, is
constant since the stimulus is also constant. The sensor is then
exposed to a vapor ("vapor on") that contains air and an analyte
that wasn't present during the baseline, causing an increase in the
chemical potential of the vapor phase. Molecules of analyte travel
from the vapor phase into the sensor, causing an increase in the
number of molecules that are sorbed in the sensor and an increase
in sensor resistance, R. When the sensor is no longer exposed to
the analyte ("vapor off") and is exposed only to air again, analyte
molecules desorb from the sensor and the sensor resistance
decreases to the baseline resistance. The sensor response is
calculated by: .DELTA.R=(R-R.sub.baseline)/R.sub.baseline. [1]
When a vapor is presented to an array of polymer-composite sensors,
the array produces a pattern, as shown in FIG. 1B, since most, if
not all, sensors in the array preferably produce different
responses. The chemical potential of a vapor component is
proportional to the percent saturated vapor pressure. (Percent
saturated vapor pressure is equivalent to relative humidity for
water content.) The chemical potential of a vapor component in the
sensor is proportional to the number of sorbed molecules and is
inversely proportional to the average interaction energy of the
sorbed molecule with the sensor materials. A change in the sensor
resistance is proportional to the change in the mass of sorbed
molecules. At equilibrium, when the chemical potentials of each
component in the vapor phase and the sensor are equal, the sensor
response follows the scaling argument:
.DELTA..times..times..about..times..times..times..times..DELTA..function.-
.function. ##EQU00001## where (.DELTA.R/R).sub.j is the sensor
response for the j.sup.th sensor in the array, .epsilon..sub.ij is
the interaction energy between the i.sup.th component in the vapor
and the j.sup.th sensor in the array, P.sub.i is the partial
pressure of the i.sup.th component in the vapor, P.sub.sat,i is the
saturated vapor pressure of the i.sup.th component in the vapor
phase at the sensor temperature, T.sub.sensor. Since the
interaction energy, .epsilon..sub.ij, is different for each
analyte-sensor pair, the response of each sensor in the array will
be different for the same vapor. The interaction energy,
.epsilon..sub.ij, is a measure of sensor sensitivity to a given
analyte and in certain aspects has values ranging nearly two orders
of magnitude for different analyte-sensor pairs. Although PCS
sensors are preferred, it is understood that sensor devices
according to the present invention may include other sensor types
in addition to, or alternatively to, PCS sensors.
U.S. Pat. Nos. 5,571,401 and 5,788,833, each of which is hereby
incorporated by reference in its entirety for all purposes,
disclose chemical sensors useful for detecting analytes in a fluid
(e.g., liquid, gas) as well as useful polymer-composite materials
for polymer-composite sensor systems and devices. U.S. Pat. No.
6,537,498, which is hereby incorporated by reference in its
entirety for all purposes, shows colloidal particles and other
materials useful in the sensors devices of the present
invention.
In one aspect, the present invention provides highly engineered
sensors created from nanometer-sized carbon black particles
stabilized with molecules or polymers attached directly to the
carbon surface. These surface-modified carbon black (SMCB) sensor
materials can be dispersed in a solvent and result in suspensions
that preserve the nanometer-scale particles where typical carbon
black/polymer dispersions aggregate at the micron size regime.
These materials are highly suitable to the low-volume jetting
processes of the present invention. In addition, the sensitivity of
these materials is equal to or greater than similar composite
sensors that do not utilize the surface modification approach.
Extending this demonstrated capability to a range of chemically
distinct sensing materials is advantageous.
Several other resistive-based sensing technologies are also
compatible with the sensor deposition techniques of the present
invention. One specific sensing technology is intrinsically
conducting polymers. While intrinsically conducting polymer sensors
have been known for some time, historically these materials have
been susceptible to moisture resulting in unreliable sensor
performance. Recently, new materials have been fabricated for
display purposes that show much greater stability to moisture.
Traditionally, these intrinsically conducting materials have high
sensitivity for certain high vapor pressure compounds including
chlorine-, ammonia-, and sulfur-containing gases.
Another class of materials that is suitable for use in the present
invention is carbon nanotubes. The chemical detection capabilities
of these materials have been recently reported (Kong, et al.,
Science, 287(5453):622 (2000)). In these reports, these materials
are manually manipulated to lie between parallel electrodes.
Furthermore, manufacturing variability of single nanotubes is very
high. By averaging behavior over a number of nanotubes, single tube
variability can be reduced or eliminated. This will lead to a more
reliable and economical manufacturing path than has been previously
demonstrated. In certain aspects, the present invention provides
methods to deposit nanotubes directly from a solvent that
completely evaporates. This approach focuses on using one or
multiple nanotubes in a, single sensor.
Another set of materials that is used in one aspect is
surface-modified colloidal metal particle sensors other than carbon
black. These include surface-modified gold nanoparticles as
chemical sensors similar to the surface-modified carbon blacks
described above. Use of these materials as biopolymer based sensors
has been demonstrated (Frey et al., Langmuir, 17(8):2408 (2001);
Ostuni et al., Langmuir, 17(9):2828 (2001); Engelkamp, Science,
284(5415):785 (1999)). These materials are often referred to as
self-assembling monolayer (SAM) sensors since alkane thiols are
often used as the surface modifier which form a monolayer on the
metal surface. In the present invention, both traditional polymer
modified gold nanoparticles and biopolymer modified gold
nanoparticles may be used as resistance based chemical and
biological sensors. The resistive read out provides a more robust
measurement compared to optical detection that requires the
alignment of lightsource, surface, and detector that currently
limits these devices to laboratory use. A second advantage is that
these materials are compatible with the sensing and deposition
methodologies of the present invention. These materials have been
demonstrated as effective sensors. The fabrication of these sensors
is generally similar to that of the carbon-black-based systems.
In addition to the surface-modified biopolymer sensor mentioned
above, there is a second emerging biodetection technology useful in
the present invention. The technology, developed at HRL (formerly
Hughes Research Laboratory), involves sol-gel encapsulated
enzyme-based sensors. These biosensors are based on conductive
polymer transducers coupled with bioindicator molecules (e.g.,
enzymes) which are encapsulated within sol-gel matrices (biogels).
These sensor elements detect analytes in water, and air (including
aerosols) and detect analytes in soil, as well. Detection is
accomplished by monitoring the change in resistance of the
conductive polymer. The power consumption is extremely low (on the
order of microwatts) so battery life is long. This sensor approach
has been utilized to detect sporylated bacteria from an aerosol at
the 1000 organism level. A key advantage of this biosensor is that
it can operate without consumables and can detect directly in
air.
In certain preferred aspects, an array of multiple, e.g., 32
sensors, is implemented in the devices of the present invention,
but arrays can be comprised of fewer sensors or even more sensors
as desired for the particular application. For certain specific
applications, an array of only four or five sensors is typically
sufficient if sensors are appropriately selected. In preferred
aspects, an array of sensors includes a single PCS sensor or
multiple PCS sensors. Also, the array may include none, one or more
other sensor types.
U.S. Pat. No. 6,085,576, which is hereby incorporated by reference
in its entirety for all purposes, discusses aspects of an example
of a handheld sensor system, which includes a relatively large
number of sensors incorporated in a handheld device that is
intended to be used for a wide range of applications. One such
sensor, the Cyranose.TM. 320 (C320), is a COTS handheld vapor
identification system that, in one aspect includes: (1) a
polymer-composite sensor (PCS) array that returns a signature
pattern for a given vapor, (2) a pneumatic system to present that
vapor to the sensor array, and (3) implementations of pattern
recognition algorithms to identify the vapor based on the array
pattern. The C320 has been successfully tested as a point detector
for TICs (e.g., hydrazine, ammonia, formaldehyde, ethylene oxide,
insecticides) as well as CWAs (e.g., GA, GB, HN-3, VX).
FIG. 3a illustrates a portable detector device 10 according to an
embodiment of the present invention. It is preferred that the
housing structure is small. Device 10 includes an array 15 of one
or more sensors, preferably one or more polymer-composite sensors
(PCS) as discussed herein. Digital signal processing (DSP) unit 20
receives and processes signals from sensor array 15 and stores data
to memory 40. Pneumatic pump system 35 is optionally provided to
assist with providing vapor to sensor array 15. In certain aspects,
alarm module 25 is included to provide an active alarm when an
alarm condition has been determined, e.g., when a programmable or
preset threshold condition or value is exceeded. Alarm 25 can
include a light such as an LED, a vibration module and a sound
emitting module, e.g., including a speaker. One or more
communication modules 30 are provided for interfacing with external
intelligence such as a central alarm system. In one aspect, a
communication module 30 includes an interface device such as an RF
transmitter (or transceiver) for transmitting RF signals to an
external device such as a command system or relay node.
Communication module 30 can also include a receiving device such as
an RF antenna (or transceiver) for receiving commands and data.
Other useful interface types include IR transmitters, Bluetooth,
RS-232, USB and Firewire interfaces, and any other wireless and
physical connector interfaces (and associated protocols) for
interfacing with external intelligence devices and systems such as
a computer system. U.S. Pat. No. 6,422,061, which is hereby
incorporated by reference for all purposes, discloses handheld
sensor systems configured to interface, e.g., wirelessly, with a
distributed network.
All components of device 10 are preferably coupled via one or more
busses, but they may be individually directly connected as suitable
for particular applications. In wearable badge device embodiments,
an attachment device 45 such as a clip, strap or a pin is provided
for attachment to a pocket, shirt lapel, belt, around the neck, etc
as is convenient or necessary for the particular application. A
battery and battery status monitor (e.g., LED light) are also
preferably included (but not shown).
FIG. 3b illustrates a portable detector device 100 according to
another embodiment of the present invention. In preferred aspects,
device 100 is portable, wearable, has low power requirements and is
self-calibrating. As shown, device 100 includes sensor interface
circuitry module 115, which is configured to receive signals from a
sensor array (not shown) and provide signals to a processor module
120 (e.g., DSP). Processor module 120 processes the received
signals as will be discussed herein to detect and identify various
environmental events or conditions. Memory 140 is used by processor
module 120 to store various data, parameters and algorithms
associated with event detection and identification. RF transceiver
module 160 is configured to transmit and receive information to and
from an external intelligence source such as a remote computer
system, a base station or node in a distributed network of sensors,
a remote alarm system, etc. Alarm module 125 includes one or more
of a visual indicator such as an LED, an auditory indicator such as
a buzzer or speaker and a vibratory indicator. Processor 120
activates alarm module 125 in response to detection and/or
identification of an alarm event. An optional display 135 is
provided to allow a user to view information related to event
detection and identification processing. Communication module 130
is included to provide a communication path to external
intelligence, whether directly connected (e.g., USB, Firewire,
RS-232) or remotely connected (e.g., wireless). It will be
appreciated that one or both of modules 160 and 130 may be
implemented on detector device 100.
Power supply circuitry module 155 is provided to control various
modes of operation of device 10. As will be described in more
detail below, for example, power supply control circuitry is
configured in certain aspects to place device 100 in a sleep mode,
or reduced power consumption mode, and to awaken device 100 and
place it in a full power consumption mode. Battery 145 is provided
as a power supply source. Battery 145 may include a conventional
battery, a solar cell or other power source. Alternatively, or in
addition to battery 145, RF Tag module 150 is provided in some
embodiments to allow for remotely powering up device 100 as will be
discussed in more detail below. An attachment device (not shown) is
also included in wearable device embodiments.
Devices 10 and 100, in certain aspects, are preferably implemented
in or on a housing structure such as a card-shaped or badge-shaped
plastic structure, or other compact structure allowing for ease of
use, transport, wearability, attachment to a user, etc. Additional
aspects of sensor devices of the present invention, such as sensor
devices 10 and 100, including portability and wearability, low
power consumption, self-calibration, and event detection and
identification will now be described with particular attention to
implementations including polymer-composite sensor (PCS) elements.
It is understood, however, that sensor elements other than PCS
elements may be additionally or alternatively used.
Sensor Interfaces
Referring to polymer-composite sensor arrays, a constant current
source is provided to deliver constant low level dc current
independent of the load. Studies indicate a significant reduction
in sensor noise with bias currents less than 100 uA. Sensors have
been shown to operate with as little as 5 10 uA. Also constant
current provides a more accurate means to detect sensor response
due to a high degree of linearity.
Low Power Consumption
Typical polymer-composite sensor elements exhibit a base resistance
of between about 2 KOhms and about 100 KOhms, nominally about 10
KOhms. The peak power consumption (per sensor element) can easily
be calculated (using a 10 uA constant current driving scheme) as
follows: Ppk=(10E-6)*(10E-6)*(10E3)=10 nW Further this number can
be reduced if the sensors do not need to be constantly active. That
is the average power: Pavg=Ppk*DF where DF is the duty_factor
representing the percentage of the conversion time/response time.
Conversion times represent the total time it takes to capture the
sensor response and process the information. The conversion times
are typically on the orders of milliseconds.
In one aspect, operation of devices of the present invention
advantageously require less than about a milliwatt of power, and
even less for certain device embodiments including only PCS
sensors. The typical lifetime of a device operating at 1 milliwatt
is on the order of approximately several weeks to several years or
more. Further, power management capabilities reduce the power
requirement as well as increase the lifetime of a power source.
One goal of wearable badge devices is optimal power management. One
embodiment of a power management method of the present invention is
shown in FIG. 22. In one aspect, the device is placed in a SLEEP or
very low power mode 200 for a significant amount of time, e.g.,
over 70%, or 80% or 90% of the time, depending on needed response
time. The processor wakes up periodically 210, for example, in
response to a wakeup signal from power supply circuitry 155, scans
220 across the sensor array and determines whether an event has
occurred or is occurring 230. If not, the processor is put back to
SLEEP 200. If an event is detected, the processor executes pattern
recognition techniques 240 to identify the event. Once identified,
the event is announced 250, e.g., either displayed, an output
signal is activated, an audible alarm is activated, etc. or all of
the above. Additional core average processing power is on the order
of uA's.
Power Source
The device can be powered by a variety of means including an
on-board battery or solar cell 145. Coin size batteries, such as
standard 3 V batteries, are particularly useful and could last 5 10
years or more. The device might also be configured with an RF or IR
tag element or module 150, whereby optical radiation or
electromagnetic energy (activation energy signal) is remotely
delivered to the device. In RF or IR tag embodiments, the device
instantaneously stores enough energy from the activation energy
signal to process information and relays this information back to
the power source. Aspects of useful RF and IR tag circuitry can be
found in U.S. Patent Application Ser. No. 60/477,624, filed Jun.
10, 2003, entitled "Chemical Passive Sensor", the contents of which
are hereby incorporated by reference.
Self-c1041 alibration
In certain aspects, the system is configured to periodically
monitor all physical channels and determine if the sensor inputs
are within the electrical operating range. If not, the system
automatically biases each sensor accordingly and adjusts its
baseline readings.
Event Detection
Event Detection is implemented to further reduce overall power
consumption. In one aspect, an event first detected, then pattern
recognition methods are used to identify the event(s). Event
detection is threshold-based in one aspect. For example, in one
aspect, once an event is detected the on-board processor is
awakened (interrupted) and one or more pattern recognition
processes are executed to identify the event.
FIG. 23 is a generic block diagram illustrating a detection process
300 and a typical response curve according to one embodiment. In
the following description of aspects of process 300, process
parameters such as delay time, average response and threshold have
been chosen based on experimental results and are only meant to be
exemplary and not limiting in any way.
Data is first collected 310 from each of the sensors, e.g., sensor
response signals are collected. Each sensor response signal
represents a resistive measurement in the case of PCS sensors. The
resistance changes depending on the type of event to which the
sensor is exposed. Each sensor element preferably responds in a
different fashion. In one aspect, the process 300 allows for a
moving base resistance; the response is the percent change from the
most recent measurement with respect to a past moving base
resistance. In one aspect, a circular buffered, backward-looking
moving average process is coded and implemented in the on-board
processor. The buffered data represents a time parameter to store
the baseline resistance of each of the channels, e.g., number of
sensors in an array.
The baseline resistance of all sensors is calculated 315. To
account for slow changes in ambient conditions, such as humidity
and temperature, and any sensor drift, the baseline resistance,
R.sub.0, is constantly updated based on recent history. There are
at least two parameters--delay time and averaging time--that can be
tuned. Since the data in one analysis was acquired over a short
period of time, the delay time (or buffer) was set at 200 points
(.about.2 minutes) and averaging time was set at 5 points.
The response of all sensors is calculated 320. In one aspect, the
response, .DELTA.R/R.sub.0, is calculated for all sensors as a
fractional change in resistance,
.DELTA..times..times..function. ##EQU00002## where R(t) is the
time-averaged resistance at the present time and R.sub.0 is the
baseline resistance collected at 2 minutes earlier. The responses
for individual sensors are used for pattern recognition to identify
an event, e.g., determine whether a disturbance is a nuisance or a
fire.
The sensor-averaged response is calculated 330: In one aspect, the
sensor-averaged response, (.DELTA.R/R.sub.0).sub.avg, is calculated
to provide a robust measurement of the presence or non-presence of
a disturbance.
The sensor averaged response is compared with a threshold value
340. In one aspect, for example, if
|(.DELTA.R/R.sub.0).sub.avg|>0.001 (or other threshold value,
e.g., 0.01), then the magnitude of the sensor-averaged response is
too large indicating that an event has been detected, e.g., a
disturbance from normal operation has been detected. The threshold
value may be preset and adjustable. It is necessary to evaluate the
magnitude of the disturbance since sensor responses increase and
decrease with a change in an environmental state or in the presence
of an environmental condition such as a fire. If no disturbance is
detected, normal operation is continued.
Pattern Recognition
Once an event has been detected 350, the processor awakes from
SLEEP (see, e.g., FIG. 22). The responses from all channels are
temporarily stored in memory, e.g., RAM, and compared to known
chemical patterns. Simple to very complex pattern recognition
techniques might be implemented depending on the application. Such
techniques include K-nearest neighbor (KNN), Canonical Discriminate
Analysis (CDA), Soft Independent Modeling of Class Analogy (SIMCA),
probabilistic neural network (PNN), artificial neural network
(ANN), support vector machine (SVM), Fisher Linear Discriminate
(FLD) and others.
In wearable badge embodiments, a detector badge would be worn by an
individual, e.g., attached to a lapel or shirt or pants pocket with
an integrated clip or pin, or worn around the neck, and when
powered on would notify the wearer of normal detector status (e.g.,
green LED, no alarm) and battery status (e.g., green/red LED).
After status check, the detector badge would monitor the
environment continuously and announce detected hazard events, e.g.,
via an audible, visual (e.g., red LED) and/or vibratory alarm.
Detector badges might also include modules for recording data and
wirelessly transmitting information such as badge ID, status
information and alarm condition information, to a central monitor
station. Detector standardization using a supplied standard to
verify proper operation, either periodically or before use, and
battery replacement or recharging are typically user maintenance
activities that may be required.
Wireless portable detectors without pneumatic system 35 can be
implemented for applications that have stringent requirements for
size, cost, power requirements and ruggedness. Such scaled down
detectors are useful as badge detectors for TICs, BWAs and CWAs.
Additionally, communication module 30 can be eliminated for badge
devices where a personal alarm is the only necessary feedback.
In certain aspects, a modular detector device is provided. For
example, a detector device or sensor module may be coupled to a
communication module. For example, a badge device in one aspect is
configured to plug into a thin communications platform that allows
the detector device to be included in a distributed network. The
platform can include wireless or wired network connections. A
sensor module can couple with any additional modules such as
pnuemnatics, communication, calibration, power recharge and other
modules. As another example, a detector device can be implemented
as a residual life indicator, e.g., by inserting the device in a
respirator cartridge as will be discussed in more detail below.
Event Detection and Analysis
In preferred aspects, digital signal processing (DSP) unit 20
incorporated in the detector device converts the sensor responses
into an actionable answer. At least three different classes of
techniques may be used, depending on the requirements of the
application. These classes are listed in increasing order of
complexity: Simple detection: Thresholds are applied to individual
sensors or globally to the responses of the entire array. When the
threshold logic is satisfied, an alarm condition is detected. For
example, if any of four sensors in an array exceeds a threshold
value, an alarm activates, e.g., alarm 25 is activated. Pattern
recognition: The response pattern from the array is compared to
patterns stored in a training set or library. When a match is
found, the identity of the vapor is returned. Useful pattern
recognition techniques include KNN, CDA, SIMCA, PNN, ANN, SVM, FLD
and others. Quantification: The response pattern from the array is
used in certain aspects to calculate the concentration of analyte
in the vapor phase.
In certain aspects these techniques can be used individually or
mixed-and-matched. For example, simple detection can be used to
detect that an event is occurring, and pattern recognition can be
used after event detection to identify the nature or source of the
event. Such a DSP methodology has been used successfully in a
passive sensor array such as in a fire detector in UL and BSI
laboratory tests.
For chemical events, the minimum detectable levels of the detector
devices are important since the IDLH level has been identified as a
requirement for consistently detecting the presence of TICs and
CWAs. In certain aspects, the minimum detectable level (MDL) of a
single sensor is measured by its detection limit. A detection limit
is a useful concept to describe the performance of an
analyte-specific sensor and is typically defined as the
concentration that yields a sensor response with a signal-to-noise
ratio equal to a threshold value (e.g., three). A detection limit
is appropriate for analyte-specific sensors since few other
chemicals could have caused the same level of response. If a
detection limit is applied to a single sensor in an analyte-general
array, any chemical could have caused the response since the sensor
does not have specificity. Discrimination limits and identification
limits are more useful concepts when describing the performance of
an analyte-general sensor array. The discrimination limit is
defined as the analyte concentration at which a method of pattern
recognition can be used to discriminate an analyte in a carrier gas
from the carrier gas alone. The identification limit is defined as
the analyte concentration at which a method of pattern recognition
can be used to consistently identify the presence of an analyte. An
identification limit is preferably used as the measurement of
performance for the MDL in certain aspects.
Since equation (2) is valid for individual polymer-composite
sensors, this equation can be used with experimental data for
chemical species to estimate the MDL of the sensor array for any
other chemical. FIG. 2 shows IDLH concentrations on a plot of
concentration versus vapor pressure for CWAs and TICs. In FIG. 2,
the sensor array has a high probability of identifying any analyte
with a symbol above the region labeled "Minimum detectable levels
for sensors in C320 (estimate)." This region will be called the
region for minimum detectable levels (RMDL). The sensor array has
moderate or low probability of identifying an analyte with a symbol
inside or below the RMDL, respectively. The further below the RMDL,
the probability of identifying the vapor decreases.
A region is preferably used for the MDLs rather than a single line
for the following reasons: Variability of environmental conditions:
Applications that have environments that are more variable tend to
have higher values for minimum detectable levels. The applications
tend to have minimum detectable limits closer to line A. Sample
variability: Applications that have analytes with significant
variability also have higher values for minimum detectable levels.
These applications typically include natural products and tend to
have minimum detectable limits closer to line A.
Application-specific sensor array: When a specific application is
identified, specific sensors can be used (or sensor responses can
be removed in software) to remove unimportant information, and
sensor performance improves. Application-specific sensor arrays
tend have lower values for minimum detectable levels closer to line
B.
For badge detector devices, the MDL is generally closer to line B
on FIG. 2. The two effects of variability are approximately equal
and have opposite effects. Since a badge detector is a field-use
device, environmental variability tends to increase the MDL, but
sample variability is small since the chemicals are well defined,
causing the MDL to decrease. Since applications tend to focus on
CWAs and some TICs, the MDL can be improved by using the most
appropriate sensor array for the application.
Tests of the C320 further validate the estimates in FIG. 2. During
controlled tests of CWAs by independent laboratories (Midwest
Research Institute and Battelle Memorial Institute), sensor arrays
in the C320 detected Tabun (GA), Sarin (GB), Soman (GD), VX, Sulfur
Mustard (HD) and Nitrogen Mustard (HN3) at or below a 9 ppbv
threshold limit. Additional testing by the U.S. Army Edgewood
Chemical and Biological Center showed the C320 correctly
discriminated GB, GD, VX, HD, Malathion and DMMP.
Detector devices according to the present invention are also
capable of identifying and discriminating narcotics, explosives
(e.g., TNT, C4, RDX, ANFO and others) and hazardous materials.
Analyte-general chemical alert devices of the present invention are
advantageously capable of detecting biological and chemical hazard
events arising from a wide range of chemical and biological classes
and are not restricted to a pre-defined short-list of just a few
TICs. In certain aspects, effects of interference and
cross-reactivity are minimized through a combination of sensor
materials and detector operational design (algorithm and hardware)
as described above using event detection, discrimination and
interferent rejection techniques. 1) Event detection: Changes in
environment (false positives) due to temperature, humidity, or
chemical background occur gradually, over minutes to hours, and are
not recognized as hazard events. Second, polymer-composite sensors
(PCS) are not dosimeters; cumulative low-level exposure over
hours/days will not trigger an alarm (unlike colorimetric
indicators). Third, the polymer-composite (PCS) sensors are stable
and less reactive to moisture than other sensors (e.g., conducting
polymers). The combination of PCS sensors and event detection helps
minimize false positive risks. 2) Discrimination: Real-time
pattern-recognition techniques are preferably used to identify
chemical classes. Although unrecognized chemicals may not register
a class alarm (false negative), a two-stage approach minimizes the
risk of false negatives by utilization of chemical event detection
followed by discrimination. In this case, even new and unknown
threat chemicals will register an event alarm for hazards above a
threshold. 3) Interferent Rejection: In addition, real-time pattern
recognition is preferably used to screen for and reject known
interferents that may otherwise register as a chemical event, e.g.,
sudden increase in moisture content due to sea spray, spills or
cleaning operations.
In wearable badge detector embodiments, polymer-composite sensor
arrays are particularly advantageous as they are preferably 1)
rugged and stable in various environments; 2) compact, lightweight
and wearable; 3) inexpensive to produce; and 4) low power
consumption systems. More detail about such advantages follows:
Rugged and Stable: Polymer-composite sensors are stable in the
presence of moisture, allowing the sensor array to operate over a
wide range of humidity (0 99%, noncondensing). PCS sensor arrays
have been tested in aqueous solutions for nearly 5,000 continuous
hours with no effect on sensor stability. The array also operates
over a wide range of temperatures. Tests have been completed over a
temperature range of -15.degree. C. to 40.degree. C. with no effect
on the sensors. Finally, the array has a long shelf life. Sensor
arrays have been stored for up to three years in an uncontrolled
environment in a laboratory, and the arrays required no special
pretreatment before use. Compact, Lightweight, and Wearable: The
chip can be implemented using dimensions of approximately
1.25''.times.1.25''.times.0.25'' with a mass of a few ounces. In
preferred aspects, the chip, and hence the device in some
embodiments, has a footprint area of less than about 4 square
inches (e.g., 2''.times.2'') and more preferably less than about 1
square inch (e.g., (1''.times.1''). The chip includes processors,
battery, and sensors. Further miniaturization can be achieved, if
required. Inexpensive: The polymer-composite sensor array is
inexpensive because the sensors are comprised of small amounts of
carbon black and COTS polymers. The direct cost for sensor
materials is very low, e.g., significantly less than $0.01. Low
Power: Polymer-composite sensors require only .mu.W of power during
normal operation. The chip can operate for at least six months or
more using a typical battery.
In one embodiment, a four channel detector, operating in a variable
humidity environment, detects transient chemical events (malodors)
of unknown composition and triggers an alarm/response via an RF
link when a programmable threshold value is exceeded. In one
aspect, no data is transmitted from the sensor, just an alarm
state. A typical response curve to a transient event is shown in
FIG. 4 for such a device, and an example of such a device is shown
in FIG. 5; the backside contains the battery and the antenna. In a
preferred badge embodiment, there is no pneumatic system and the
detectors are continuously exposed to the environment.
Fire Detection and Prevention
In certain aspects, devices according to the present invention are
particularly useful in fire detection and prevention activities. In
such embodiments, devices of the present invention preferably
include a PCS array and one or more additional sensor modules such
as a photodetector, an ionization detector and a thermal detector.
Published PCT Application WO00/79243, which is hereby incorporated
by reference for all purposes, discloses sensor systems including
multiple sensor types which are useful for fire detection and
prevention applications as well as for other detection applications
as described herein. Signals from the PCS array and other included
sensors are monitored and processed by an algorithm configured to
detect events and nuisances and discriminate between fire sources
and nuisance sources with a high degree of confidence so as to
reduce the occurrence of false positives. FIG. 6 shows an example
of a fire detection system including detection devices according to
an embodiment of the present invention.
Many current chemical sensor arrays can discriminate different
types of fires after the fire has been active for a long period of
time. However, this use-model is not adequate for fire detection
since time is of the essence. According to the present invention,
an algorithm detects an event as early as possible and immediately
identifies the event as a nuisance or fire. In the section
following, examples of fire and nuisance data are disclosed:
Fire & Nuisance Data
TABLE-US-00001 TABLE 1 Fire tests that were completed in fire room.
UL Fire Tests BSI Fire Tests Non-Standard Fire Tests Gasoline 1
Alcohol 1 Dense plastic fabric Gasoline 2 Alcohol 2 Flaming cotton
fabric Heptane 1 Cotton 1 Plastic curtain Heptane 2 Cotton 2
Smoldering cotton 1 Paper 1 Flaming Wood 1 Smoldering cotton 2
Paper 2 Flaming Wood 2 Smoldering linen & plastic Polystyrene 1
Heptane 1 Smoldering paper 1 Polystyrene 2 Heptane 2 Smoldering
paper 2 Smoldering Wood 1 Polyurethane 1 Smoldering paper 3
Smoldering Wood 2 Polyurethane 2 Smoldering cotton fabric Wood Crib
1 Smoldering Wood 1 Wood Crib 2 Smoldering Wood 2 Smoldering
TABLE-US-00002 TABLE 2 Nuisance tests. Series 1 Series 2 Bacon,
open door Bacon Cigarette on pillow Cigarette 1 Floor buffing
Cigarette 2 Fries cooking Cigarette puffs Oil, open door Dry air
freshener Oil Enamel Sour craut Nilotron Steam Popcorn Sugar
Rustoleum Vamish Wall Paint
In one embodiment, simple detection is used to detect that an event
is occurring, and pattern recognition is then used to identify the
nature of the event. This two-tiered algorithmic approach for
detecting and identifying events works well for polymer-composite
sensor arrays. The first algorithm simply detects that an event
occurs. All fires must be detected, and, ideally, no nuisances
would be detected. But it does not matter whether the event is a
fire or a nuisance at this point because the second algorithm is
used to differentiate between these two groups of events.
There are several parameters in the detection algorithm that are
preferably optimized so that all fires are detected and a minimal
number of nuisances are detected.
These parameters include:
type and number of sensors used for averaging; number of points
used for time averaging; number of points in the buffer (delay
time); the number of consecutive points outside the threshold; and
the value of the detection threshold.
A typical response is shown in FIG. 7 using an array of 32 PCS
sensors when all 32 sensors are used and the number of points in
the buffer is a parameter. The parameter had little effect on the
detection time, but the number of buffer points drastically
affected the overall magnitude of the response.
Once an event is detected, the second part of the algorithm
identifies the nature of the event as a fire or a nuisance. FIG. 8
illustrates a model using Soft Independent Modeling of Class
Analogy (SIMCA).
Additional useful algorithms are disclosed in U.S. patent
application Ser. No. 10/112,151, filed Mar. 29, 2002, the contents
of which are hereby incorporated by reference for all purposes.
Protective Absorption Based Filters
In certain aspects, devices of the present invention are useful in
protective absorption based filter systems. The actual useful life
of a protective absorption based filter is a function of the amount
of absorbent material, the absorbent-sorbed species interaction,
and the concentration and duration of the exposure. Since this data
is almost always unknown, the manufacturers' recommendations and
civilian and military specifications are based on a few marker
chemicals and test scenarios and offer only a rough guide as to
when to replace or regenerate the filter. In most cases as well,
the end user does not know when the exposure starts or ends, and
what chemical's biologic agents and concentration levels are
present in the environment. Sensor devices of the present invention
incorporated into a filter or pneumatic pathway can provide a
timely warning to the user that the absorptive capacity of the
filter has reached a pre-defined level. This allows users to exit
the hazardous area and replace or regenerate the media and reduce
the potential hazard to these personnel. Accordingly, in one
aspect, the present invention provides polymer-composite sensor
arrays in protective air filtration systems so as to provide
low-cost, low power, lightweight, rugged, stable, and accurate
residual life indicators for personal protective air filtration
systems for Volatile Organic Chemicals (VOCs), biological agents
and other hazardous materials. Such systems are useful in, for
example, filter breakthrough systems, indoor air quality
applications, cabin air systems, personnel protective equipment and
motor vehicles.
In one embodiment, multiple miniature sensor devices are positioned
at various depths in a filter bed such that successive sensor
detection of a breakthrough event (at the IDLH) level and
subsequent alarm outputs correspond to consumption of the
absorptive capacity, hence indicating residual life. The final
sensor is preferably placed appropriately to permit some exit time
from the hazardous area without undue wastage of filter
cartridges.
FIG. 11 illustrates a schematic representation of a Residual Life
Indicator Fixture according to an embodiment of the present
invention. As shown, detectors are sequentially positioned within a
filter bed by embedding detectors in filter material in a gas flow
path. Inlet and approximate stage-wise analyte concentration is
monitored semi-continuously by Gas Chromatography and continuously
by sensor output. The upstream sensor (1) responds to the presence
of the analyte when the first Filter Bed experiences breakthrough
while the still protected downstream sensors (2) and (3) do not
respond. This is analogous to consumption of 1/3 of the filter
system capacity (2/3 Life Remaining). As flow continues, downstream
sensor (2) responds as the second Filter Bed experiences
breakthrough; this corresponds to consumption of 2/3 of the filter
system capacity (1/3 Life Remaining). The final filter bed also
serves as the gas scrubber. The approximate stage-wise
concentration in the filter bed is preferably monitored by Gas
Chromatography as well as by the polymer-composite sensor
system.
FIG. 9 illustrates examples of chemical filter systems for which an
end-of-service-life indicator (ESLI) module including one or more
PCS sensors is useful.
FIG. 10 illustrates a system including a distributed network of
wireless sensor devices according to the present invention. The
sensors shown can be implemented in air filtration or detection
systems or as stand-alone devices positioned as desired. In one
aspect, a population of sensing devices may be distributed randomly
or in known locations to form a network. Each such device
preferably includes a transceiver or other wireless communication
module for communicating information signals to a base intelligence
node, such as a central processing node, central computing device
or distributed network of computers and or processing nodes. The
base intelligence node receives and processes signals received from
the various sensing nodes and provides valuable information
therefrom to an operator, or may automatically activate an alarm if
a threshold condition is met. In some aspects, the sensing devices
include GPS (global positioning system) location modules or other
location determining modules to determine the locations of the
devices. Location determining modules are particularly useful where
sensing devices are randomly distributed, e.g., dropped from an
airplane or otherwise randomly, geographically distributed, and it
is desirable to associate a precise (previously unknown) location
with a detected event, agent or environmental parameter. For
example, a growing risk of asymmetric attacks has increased the
need for distributed biological detectors with superior false
positive rates relative to current solutions. The low cost, low
power and highly sensitive chemical and biologic detectors of the
present invention are capable of continuous distributed monitoring
of biological warfare agents (BWAs) and will advantageously provide
for improved monitoring of biological threats.
In one aspect, software processes are provided for both low level
and high-level control of node function, for aggregating and
interpreting sensor data at a single node, and for calibrating
devices at the point of manufacture and in the field. In another
aspect, a pattern matching approach is used to detect and identify
compounds from a library. This library may reside either on the
device or at a remote location. This approach allows for rapid
upgrading of instruments as new threats become important.
A network of autonomous sensors reporting to a central location
offers the potential to further false alarm reduction and improved
alarm prediction through software processes deployed at the network
level. In one aspect, therefore, processes are provided for sensor
data fusion. One module of this system is a symbolic data model
that reads discrete data (e.g. alarms, settings) and applies two
different mathematical approaches to identify anomalies. In the
first case, a set of rules is applied to this data to generate
derived states and anomalies. While the mathematical analysis
process may be generic, the set of rules must be determined for a
given application so the SDM is best described as a
"knowledge-based" component. For example, this portion should
operate on rules such as: if alarm A sounds do nothing unless alarm
B sounds. In addition to this rules based module, a second module
is provided in some aspects which uses more advanced mathematical
tools to identify anomalies. This module, in one aspect, utilizes
Hidden Markov Models (HMM) to identify anomalies based on
probabilities of passing from one state to a second state. The HMM
may use different algorithms to define these probabilities such as
a Viterbi algorithm, a forward-backward algorithm, or a Baum-Welsh
algorithm. All of these methods are designed to find hidden
patterns in data. The output is the prediction of an anomaly based
on a number of different discrete state variables.
In networked systems, various network protocols may be used, such
as for example, point-to-point, point-to-multi-point, and others.
Devices and nodes may be individually addresses, and different
networks may use a different pseudo-random hopping sequence. To
prevent interfering collisions from different networks, modules may
be configured to jump to different frequencies.
FIG. 12 illustrates a mask-based filter interface system including
a detector device module according to an embodiment of the present
invention. The filter interface system communicates with the
filter-based detectors and provides status/alarm output to the user
based on filter status. The filter interface module is preferably
configured to be mounted on the facemask and to contain the
batteries, the signal processing circuitry and/or software and the
visual and auditory alarms to indicate the status of the filter.
Such placement allows the durable electronics to be placed in the
mask and reused, thereby minimizing the operating cost (filters) of
the system. Battery power usage is minimized while providing both
visual and auditory cues to increase assurance of user notification
in a noisy industrial environment. Size and weight is
advantageously minimized using the detector devices of the present
invention so as to not increase user discomfort and discourage use
of the enhanced protective system.
In one embodiment, the present invention provides automated
laboratory systems for detection of biologic agents. In one aspect,
an automated inoculation and growth system is provided to interface
with the existing BioWatch network and a wireless infrastructure is
provided to communicate relevant information back to a central
location. In another aspect, a laboratory system is provided which
automates the inoculation and growth of collected samples, measures
these samples with an array based sensor and uniquely reports the
presence and identity of the micro-organisms with high
reliability.
Laboratory identification of bioterrorism agents typically requires
confirmation by visual and chemical means. Standard procedures
require growth of live cells for 24 to 48 hrs followed by
examination of the developed colonies for particular morphological
(size, shape) and chemical characteristics (gram+/-stains,
antibiotic susceptibility). While this technique is time consuming,
it is the "gold standard" for positive confirmation of a biological
agent.
It is well known that growing micro-organisms produce metabolites
that are characteristic of the growing organism. This
identification of micro-organisms from their growth metabolites has
traiditonally been accomplished using gas chromatography (GC)
and/or mass spectroscopy (MS). Recently, Cyrano has demonstrated
that measuring the volatile metabolites of cell growth using a hand
held array based detector can also be used for discriminating B.
anthracis (BA) in tests conducted by the Midwest Research Institute
on standard growth medium (TSA). The test results show detection in
as little as 3 hours using standard growth media is feasible.
Discrimination from other bacteria species (E. coli) and negative
controls was also clearly demonstrated. See FIG. 24a. A new medium,
3AT, was developed for rapid growth and isolation of BA by the Air
Force Research Laboratory (WPAFB, Ohio). Medium 3AT produces a
five-fold increase in BA growth rate, yielding 24 hrs growth in as
little as 5 6 hrs. Combined with the prior Cyrano results,
detection of BA from spores is possible in less than 1 hour.
Further refinements of the medium may be possible to yield even
faster results and specific growth of Bacillus species, to the
exclusion of other spore-forming bacteria and non-bacterial
microorganisms. The technique is also easily extended to other
micro-organisms.
Biological samples are already being collected as part of the
BioWatch program. This system requires daily manual retrieval of
filters which are analyzed in the CDC's Laboratory Response Network
(LRN) laboratories. The standard analysis to confirm the presence
of a wide range of biological warfare agents (BWAs) is
microbiology. These protocols are publically available. In one
aspect, this microbiological assay is used as the underlying
detection means in a near real time system. The collected samples
from the BioWatch system are grown in highly optimized growth media
designed to rapidly promote the growth of BWAs while suppressing
growth of traditional micro-organisms. The metabolites are measured
from the headspace above the growth media at defined intervals
after inoculation. Testing begins, in one aspect, 30 minutes after
inoculation and continues for up to 24 hours. In this way, the
initial answer that may be generated at very short time frames can
automatically be confirmed on the same sample. Since continued
growth generally leads to larger populations of the target
bacteria, any initial alarms can be tracked and verified.
Furthermore, because the technique uses standard microbial growth
as the basis for the measurement, laboratory confirmation of any
suspected positive result will not require any additional time for
growth or amplification of the suspected micro-organism. Also,
samples can easily be stored in the same growth media for up to
five days and the organisms will still be viable.
In one aspect, current state of the art growth media is used to
determine the earliest possible detection of agents, e.g. 20 agents
from the CDC's Category A and B agents list. For each agent, growth
media and growth conditions are optimized and the chemical nature
of the metabolites is determined by GC or GC/MS. Simultaneous with
the analytical assessment, measurements of headspace metabolites
will also be carried out using nanocomposite array based sensor(s).
The GC/MS data is then utilized to further optimize the sensors on
the array and to determine optimal measurement times for the array.
These measurements may be carried out as a function of time, growth
media, initial inoculum size, and growth conditions. Results for
live bioagents or simulants can be compared with samples obtained
from environmental sampling and receiver operator characterization
(ROC) curves can be produced and a false positive and false
negative rate can be calculated.
In one aspect, a mechanical system is provided for automated
inoculation, storage, and measurement. Since the amount of
headspace required for measurement can be very small (<3 ccs),
in one aspect, the system uses a titer plate like geometry as
growth wells. In this way, standard pick and place instrumentation
developed for high scale laboratory testing may be utilized as part
of the system and any new development of mechanical tasks will be
minimized. Since both aerobic and anaerobic growth may be required
for each sample, the system makes provisions for providing all
necessary growth conditions to create rapid and reliable bacterial
growth.
In one aspect, an integrated laboratory system is provided that
takes collected samples, introduces them into a growth media in a
titer plate, automatically delivers the titer plate to a growth
chamber and determines the nature and identity of any
micro-organism growth. Samples with 0 10,000 organisms may be
generated and time to positive prediction may be determined for
multiple BWAs, e.g., at least 10 BWAs or BWA simulants. Receiver
operating characteristics (ROC) curves may be generated.
Sensor Arrays
In certain aspects, multiple sensor types are integrated into a
high density platform, preferably on a silicon chip, or other
substrate material as is well known. In preferred aspects, the
sensors are integrated onto a single chip. In addition to
polymer-composite and conducting polymers, useful sensor materials
include, for example, nanoscale polymer composites, carbon nanotube
composites, nanogold composites, intrinsically conducting polymers,
sol-gel biosensors based on intrinsically conducting polymers
(e.g., sol-gel encapsulated enzyme based sensors), biopolymers such
as self assembling monolayer (SAM) materials and others.
Advantages of such high density arrays include the ability to
construct systems with largely varying sensor properties, and the
ability to include a high degree of redundancy (both features of
the human system). One significant benefit of redundancy is root n
noise reduction, where n is the number of identical sensor
elements. For example, the inclusion of 64 identical sensors
produces an overall signal to noise ratio approximately 8 times
that of a single sensor (see FIG. 13). Sensor arrays that are at
least an order of magnitude more sensitive than those previously
produced can thus be achieved through the incorporation of high
degrees of redundancy. Such redundancy also has additional benefits
in terms of long-term stability and overall robustness of the
system.
According to one specific embodiment, an array comprises 900 sensor
elements (e.g., 30.times.30), but it should be understood that
arrays with fewer (e.g., one or several) or more (e.g., on the
order of 10,000 sensor elements (e.g., 100.times.100)) or more may
be implemented. In one aspect, 50 .mu.m.sup.2 sensor elements with
a 50 .mu.m inter-sensor spacing are used. This yields a sensor die
that is approximately 30 mm.sup.2 for 900 sensor devices
(approximately 1 cm.sup.2 for 10,000 sensor devices). Devices with
arrays preferably operate on a simple row-column addressing scheme
with data being multiplexed off chip for A/D conversion and further
processing, although other addressing schemes may be used. An
example of addressing is shown in FIG. 13. In one aspect, sensors
are read serially one at a time. As array sizes increase, more
off-chip bandwidth is typically required to ensure latency between
sensor readings is minimized. Sensors can then be read out in
parallel, for example, a whole row at a time. Other, more advanced
schemes for reading out sensors such as "address event" coding may
be used. In this method, "important" sensors (i.e., those that are
activated) are read out first, and more frequently than other
non-activated sensors.
FIG. 15 shows a test unit sensor cell according to one embodiment.
The cell as shown is preferably fabricated using a 2 micron CMOS
process. The sensor cell includes a switch transistor and decoding
logic. In one aspect, transistors at each sensor cell perform
decoding, primarliy due to only two metal layers in the IC process.
Circuitry M1 M4 decodes X and Y selection signals generated by
shift registers on the periphery of the array. The selection
signals control a switch (M7) that toggles a current (Iin) through
the resistive sensor element. In one aspect of this design, only
one sensor is energized at a time to reduce power consumption. To
reduce noise and the switch resistance, transistor M7 occupies most
of the sensor area. The decoding circuitry also selects a
transmission gate (e.g., M5, M6, M8, M9) which passes the sensor
voltage to a column output bus. This signal is preferably amplified
and transmitted off-chip for processing, although on-chip
processing may be performed.
FIGS. 16 and 17 show a typical I-V response of such a cell as shown
in FIG. 15, and the response of the cell to an exposure of
octanol.
In one embodiment, analog circuitry is included to provide gain at
the sensor, baseline tracking, and ratiometric sensing. Ratiometric
sensing enables a direct readout of the key metric .DELTA.R/R, that
is, the change in resistance due to the chemical or biologic agent
interaction divided by the baseline resistance, without having to
calculate this in the microprocessor. FIG. 18 shows an adaptive
bias circuit 200 according to one embodiment of the present
invention. Circuit 200 provides baseline tracking, ratiometric
output and ac coupling in one simple analog circuit.
Although aluminum can be used for conductive traces and leads, it
is preferred that an electroless gold procedure is used to produce
traces and leads due to the oxidation of aluminum over time. Other
conductive may be used.
In one aspect, the present invention provides deposition techniques
to efficiently deposit up to thousands of unique sensors in a small
area, using for example, ink jetting approaches. Accordingly, the
following focuses on useful, jettable formulations, such as
formulations of surface-modified carbon black sensors,
intrinsically conducting sensors, surface-modified nanoparticle
metal sensors, and nanotube based sensors for ink jetting. Once a
formulation exists, physical deposition onto a substrate is
performed. In one aspect, ink jetting using known ink jet heads is
preferably used for deposition. Use of a positioning system that
provides x, y and z control of the ink jet head to the micron level
is preferred. One such system is provided by Cambridge technologies
(formerly Litrex). This system allows for customization of ink jet
head and positioning of drops to within 1 micron. This system also
provides for layering of drops to build structures such as those
required in biogels. The control parameters are determined by the
physical characteristics of the formulation, e.g., relationship
between drop volume, drying rate (as controlled by substrate
temperature and solvent composition), and solids content on
deposition consistency as determined by initial resistance.
In certain aspects, a number of surface modified carbon black
(SMCB) materials are optimized for chemical and biological sensing.
These materials can be produced using a process disclosed in U.S.
Pat. No. 6,336,936, and PCT published application WO 01/50117,
which are hereby incorporated by reference for all purposes. This
process creates a direct chemical attachment of a molecule or
polymer to the surface of a carbon black particle. This process
results in a highly dispersible particle in the nanometer size
regime (e.g., 100 nm is typical), with the chemical differentiation
built into the attached organic fragment. It has been demonstrated
that these materials have superior sensing properties as compared
to chemically similar two-phase (carbon black dispersed in polymer)
sensors. In one aspect, this process is used to produce surface
modified carbon nanotubes with enhanced dispersion quality
In one aspect, four SMCB materials are used which are dispersible
in chemically different solvents. These are listed in the table
shown in FIG. 19. These materials have been demonstrated to be
stable at the nanometer size regime and are excellent ink jetting
candidates. Other useful ink-jetting materials and jettable
formulations include surface modified gold nanoparticle
formulations and nanotube formulations. Such formulations
preferably have solid to solvent ratios in the range of about 0.1
5% solids, although greater or lower ratios may be used depending
on the formulation, desired ink jetting quality and dispersion
stability characteristics.
Solutions and dispersions of intrinsically conducting polymers may
also be deposited. Such materials preferably complement the sensing
characteristics of the sensors described above. Preferred
conductive polymers include polyaniline and polythiophene(s), whose
structures are shown in FIGS. 20(a) and (b). During the conversion
of these polymers to their conducting state, an anion (or
counterion) is formed either as the conjugate acid following
protonation of polyaniline, or as an anion of the oxidizing agent
in the case of polythiophene. It has been demonstrated that the
structure and stoichiometry of these counterions play an important
role in the selectivity and sensitivity of the conductive polymer
to various VOCs.
Other sensor materials include enzyme-based biogel sensors.
Literature reports establish the feasibility of immobilizing
enzymes and other proteins in stable, porous, silica glass matrices
via an encapsulation process involving sol-gel synthesis methods.
For example, as disclosed in U.S. Pat. No. 5,200,334, which is
hereby incorporated by reference in its entirety, copper-zinc
superoxide dimutase, cytochrome c, and myoglobin can be immobilized
using mild conditions such that the biomolecules retain their
characteristic reactivities and spectroscopic properties. One key
feature in synthesizing this new type of material, termed here as
biogel, is the flexible solution chemistry of the sol-gel process.
Research in this area has emerged rapidly throughout the world and
it is now well established that a wide range of biomolecules retain
their characteristic reactivities and chemical function when they
are confined within the pores of the sol-gel derived matrix (Avnir
et al., Chem. Mater., 6:1605 (1994); Dave et al., Anal. Chem.,
66:1120A (1994)). Such an encapsulation process is shown
schematically in FIG. 21.
In addition to extending the sol-gel encapsulation process to
numerous other enzymes and other proteins, researchers have
expanded the types of biomolecular dopants to include antibodies
(J. Livage, et al, J. Sol-Gel Sci. Technol. 7, 45 (1996)) cells,
(E. J. A. Pope, et al, J. Sol-Gel Sci. Technol. 8, 635 (1997)), and
even photosystems (B. C. Dave, et al, Mat. Res. Soc. Symp. Proc.
435,565 (1996)). It is important to emphasize that the biomolecules
are physically immobilized and not covalently attached to the
inorganic matrix and, therefore, the ability to incorporate
biomolecules in the gel requires only that the synthetic conditions
do not cause protein aggregation or denaturation (J. M. Miller, et
al, J. Non-Crystalline Solids 202, 279 (1996)). In general, this
means that the sol should have minimal alcohol content and pH near
7. The inclusion of the biomolecule in the starting sol leads to a
"templating" effect where the inorganic network grows around the
dopant molecule. For this reason, a larger biomolecule is
immobilized in the matrix while smaller molecules and ions are free
to flow through the porous network. Thus, the microstructure of the
sol-gel glass is tailored so that large protein macromolecules are
immobilized in the matrix while analytes are free to enter and
diffuse through the porous network. Physical entrapment without
chemical modification preserves protein structure and functionality
and protects the protein from unfolding (denaturation). The unique
advantages of sol-gel immobilization include (1) an easy, simple,
more universal method as chemical modification is not necessary,
(2) increased durability and ruggedness as these materials can be
handled without damage to the biomolecules, (3) more flexibility in
sensor design as biologically active materials can be prepared as
bulk monoliths or as thin films, and (4) increased stability as the
biomolecules are physically, chemically, and microbially protected
by a glass matrix. This increased stability due to encapsulation in
a porous silica glass may be the most important benefit of the
sol-gel approach. The thermal stability was also enhanced, as
thermal denaturation did not occur in the silica-encapsulated
sample until 95.degree. C., whereas denaturation occurred near
65.degree. C. in aqueous buffer. A substantial improvement in the
stability of enzymes has also been observed. In studies with
butyrylcholinesterase, greater than 80% of enzymatic activity was
retained in sol-gel encapsulated samples after 40 days in the
absence of preserving agents. In contrast, under the same
conditions, enzymatic activity was almost completely lost after
about 20 days in aqueous buffer. A remarkable increase in enzyme
stability has been reported by Chen, et. al., (Q. Chen, et al, J.
Am. Chem. Soc. 120, 4582 (1998)) where the half-life of glucose
oxidase at 63.degree. C. in a sol-gel silica matrix was 200 times
longer than that in aqueous buffer. These results indicate that
tremendously enhanced stability of encapsulated bioindicator
molecules can be achieved over other reported immobilization
techniques, leading to extended device lifetimes. A further
advantage of this technique is that liquid nutrient is
co-encapsulated with the bioindicator molecule so that the latter
can retain its vitality, but the final composition is truly a solid
state device and is dry to the touch and the encapsulated materials
do not leach from the matrix. Methods to control and modify the
pore size have been reported so that analytes that are relatively
large can flow through the matrix and interact with the immobilized
bioindicator molecule.
Previous reports indicate that sol-gel materials containing
physically immobilized bio-molecules can function as the active
element or transducer for optical sensing applications. See, e.g.,
D. Avnir, et al, Chem. Mater. 6, 1605 (1994); E. H. Lan, et al,
Mat. Res. Soc. Symp. Proc. 330, 289 (1994); K. E. Chung, et al,
Anal. Chem., 67, 1505 (1995); S. A. Yamanaka, et al, Chem. Mater.
4, 495 (1992); S. A. Yamanaka, et al, J. Sol-Gel Sci. Technol. 7,
117 (1996); and S. A. Yamanaka, et al, J. Am. Chem. Soc. 117, 9095
(1995). In one aspect, devices of the present invention include
chemical sensors based on sol-gel glasses doped with enzymes
coupled with conductive polymer transducers. These novel materials
serve as chemical transducers for a new generation of devices that
utilize the molecular recognition processes inherent in
biomolecular function and thus provide extraordinary selectivity
and sensitivity. Researchers at HRL have recently demonstrated that
these sensors respond to aerosolized sporylated bacteria directly
without the need for chemical treatments or chemical
amplification.
Applications
In addition to the sensor device applications mentioned above, in
certain aspects, devices according to the present invention can be
used to detect and analyze events and conditions in a wide variety
of commercial and non-commercial applications including, but not
limited to: applications in industries such as utility and power,
oil/gas petrochemical, chemical/plastics, automatic ventilation
control (cooking, smoking, etc.), heavy industrial manufacturing,
environmental toxicology and remediation, biomedicine,
cosmetic/perfume, pharmaceutical, transportation, emergency
response and law enforcement; detection, identification, and/or
monitoring of combustible gas, natural gas, H.sub.2S, ambient air,
emissions control, air intake, smoke, hazardous leak, hazardous
spill, fugitive emission, hazardous spill; beverage, food, and
agricultural products monitoring and control, such as freshness
detection, fruit ripening control, fermentation process, and flavor
composition and identification; detection and identification of
illegal substance, explosives, transformer fault, refrigerant and
fumigant, formaldehyde, diesel/gasoline/aviation fuel,
hospital/medical anesthesia & sterilization gas; telesurgery,
body fluids analysis, drug discovery, infectious disease detection
and breath applications, worker protection, arson investigation,
personal identification, perimeter monitoring, fragrance
formulation; and solvent recovery effectiveness, refueling
operations, shipping container inspection, enclosed space
surveying, product quality testing, materials quality control,
product identification and quality testing.
For example, one recent concern is the intentional release of
chemical or biological materials as part of a terrorist activity.
While many of the detection attributes are similar between
intentional and unintentional release, there may be several key
differences. First, the level of leak in an intentional release is
likely to be very large, however, the location of the leak is
likely to be unknown. Second, the types of materials in the two
scenarios are likely to be different (specifically designed
chemical or biological agents in the case of an intentional
release). The terrorist scenario may require a very large number of
very low-cost devices to be deployed at relatively high density in
high profile target areas (e.g., public areas such as a stadium,
subway, etc.). Sensor devices according to the present invention
are very well suited to this application area and will provide a
great benefit to homeland security.
Sensor devices and arrays of the present invention are also
effective in noninvasive disease diagnostics, for example, by the
evaluation of chemical markers in breath or other bodily fluids
(e.g., blood and urine). The entire field of metabolomics,
correlating biochemical metabolites to disease, is growing in
importance. One application is the diagnosis of ventilator
associated pneumonia (VAP), a disease that effects many individuals
on long term (>48 hour) breathing support. The mortality rate
for this disease is high (>25%), owing partly to poor early
diagnosis. Low-density (e.g., n=32) chemical sensor arrays have
demonstrated a high degree of correlation between breath-based
diagnosis and traditional diagnositic measures (composite of
temperature, culture, radiography, WBC, RBC) (see FIG. 24). The
high density arrays of the present invention would further improve
this diagnostic capability and provide for others. Clinical studies
are undergoing on a variety of pulmonary disease states with The
Cleveland Clinic Foundation including asthma, cystic fibrosis, ARDS
(acute respiratory distress syndrome), COPD (chronic obstructive
pulmonary disease), and lung cancer. COPD is one of the most common
causes of death in the United States, and unlike all other most
common killers, the percentage of individuals dying from COPD is
actually on the increase (while cancer and heart related deaths are
decreasing).
Additional Sensor Types
In certain aspects, devices of the present invention may include
many different sensor types in addition to, or in place of, PCS or
other chemical sensors. Such additional sensor types include, for
example, radiation detection (e.g., geiger, scintillation, solid
state), chemical, nuclear, explosive, biological (e.g., DNA,
oligonucleotide, antibody-antigen, enzyme reaction, etc) fire
detection, and other sensor types. Suitable sensors for the systems
and devices of the present invention can also include, but are not
limited to, one or more of a conducting/non-conducting region
sensor, a SAW sensor, a quartz microbalance sensor, a conductive
composite sensor, a chemiresitor, a metal oxide gas sensor, an
organic gas sensor, a MOSFET, a piezoelectric device, an infrared
sensor, a sintered metal oxide sensor, a Pd-gate MOSFET, a metal
FET structure, an electrochemical cell, a conducting polymer
sensor, a catalytic gas sensor, an organic semiconducting gas
sensor, a solid electrolyte gas sensor, and a piezoelectric quartz
crystal sensor. It will be apparent to those of skill in the art
that the devices of the present invention can include combinations
of one or more of the foregoing sensors and sensor types.
In certain embodiments, an additional sensor can include a single
sensor or an array of sensors capable of producing a second
response in the presence of physical stimuli. The physical
detection sensors detect physical stimuli. Suitable physical
stimuli include, but are not limited to, thermal stimuli, radiation
stimuli, mechanical stimuli, pressure, visual, magnetic stimuli,
and electrical stimuli.
Thermal sensors can detect stimuli which include, but are not
limited to, temperature, heat, heat flow, entropy, heat capacity,
etc. Radiation sensors can detect stimuli that include, but are not
limited to, gamma rays, X-rays, ultra-violet rays, visible,
infrared, microwaves and radio waves. Mechanical sensors can detect
stimuli which include, but are not limited to, displacement,
velocity, acceleration, force, torque, pressure, mass, flow,
acoustic wavelength, and amplitude. Magnetic sensors can detect
stimuli that include, but are not limited to, magnetic field, flux,
magnetic moment, magnetization, and magnetic permeability.
Electrical sensors can detect stimuli which include, but are not
limited to, charge, current, voltage, resistance, conductance,
capacitance, inductance, dielectric permittivity, polarization and
frequency.
In certain embodiments, thermal sensors are suitable for use in the
present invention. Such thermal sensors include, but are not
limited to, thermocouples, such as a semiconducting thermocouples,
noise thermometry, thermoswitches, thermistors, metal
thermoresistors, semiconducting thermoresistors, thermodiodes,
thermotransistors, calorimeters, thermometers, indicators, and
fiber optics.
In other embodiments, various radiation sensors are suitable for
use in the present invention. Such radiation sensors include, but
are not limited to, nuclear radiation microsensors, such as
scintillation counters and solid state detectors, ultra-violet,
visible and near infrared radiation microsensors, such as
photoconductive cells, photodiodes, phototransistors, infrared
radiation microsensors, such as photoconductive IR sensors and
pyroelectric sensors. Optical sensors also detect visible, near
infrared and infrared waves. In certain other embodiments, various
mechanical sensors are suitable for use in the present invention
and include, but are not limited to, displacement microsensors,
capacitive and inductive displacement sensors, optical displacement
sensors, ultrasonic displacement sensors, pyroelectric, velocity
and flow microsensors, transistor flow microsensors, acceleration
microsensors, piezoresistive microaccelerometers, force, pressure
and strain microsensors, and piezoelectric crystal sensors.
In certain other embodiments, various chemical or biochemical
sensors are suitable for use in the present invention and include,
but are not limited to, metal oxide gas sensors, such as tin oxide
gas sensors, organic gas sensors, chemocapacitors, chemoidiodes,
such as inorganic Schottky device, metal oxide field effect
transistor (MOSFET), piezoelectric devices, ion selective FET for
pH sensors, polymeric humidity sensors, electrochemical cell
sensors, pellistors gas sensors, piezoelectric or surface
acoustical wave sensors, infrared sensors, surface plasmon sensors,
and fiber optical sensors.
Various other sensors suitable for use in the present invention
include, but are not limited to, sintered metal oxide sensors,
phthalocyanine sensors, membranes, Pd-gate MOSFET, electrochemical
cells, conducting polymer sensors, lipid coating sensors and metal
FET structures. In certain preferred embodiments, the sensors
include, but are not limited to, metal oxide sensors such as a
Tuguchi gas sensors, catalytic gas sensors, organic semiconducting
gas sensors, solid electrolyte gas sensors, piezoelectric quartz
crystal sensors, fiber optic probes, a micro-electro-mechanical
system device, a micro-opto-electro-mechanical system device and
Langmuir-Blodgett films.
In another embodiment, the present invention includes detection
using sensors as disclosed in U.S. Pat. No. 5,814,524, which issued
to Walt, et al., on Sep. 29, 1998, and which is hereby incorporated
by reference in its entirety. An optical detection and
identification system is disclosed therein that includes an optic
sensor, an optic sensing apparatus and methodology for detecting
and evaluating one or more analytes of interest, either alone or in
mixtures. The system comprises a supporting member and an array
formed of heterogeneous, semi-selective polymer films which
function as sensing receptor units and are able to detect a variety
of different analytes using spectral recognition patterns. Using
this system, it is possible to combine viewing and chemical sensing
with imaging fiber chemical sensors.
In certain sensor network embodiments, devices of the present
invention can include one or more sensors of similar or different
type. Also, individual nodes, e.g., individual physical device
locations, in a network of nodes can each include one or multiple
sensor types. For example, a network may include one person that is
wearing a (wireless) device including a single sensor type, a
second person that is wearing a (wireless) device including several
sensors of the same or different type, a stationary device
(wireless or direct connected) that may include one or more sensors
of the same or different type, and a network monitor station.
While the invention has been described by way of example and in
terms of the specific embodiments, it is to be understood that the
invention is not limited to the disclosed embodiments. To the
contrary, it is intended to cover various modifications and similar
arrangements as would be apparent to those skilled in the art. For
example, devices according to the present invention may be used to
diagnose diseases using appropriate sensor configurations and
analysis algorithms. Therefore, the scope of the appended claims
should be accorded the broadest interpretation so as to encompass
all such modifications and similar arrangements.
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